A rare Alaskan shorebird, rarely spotted in the southern hemisphere, was seen in Australia for the first time last summer, surprising bird researchers around the world.

Now twitchers are wondering, will the "enigmatic" Aleutian tern return down-under again this year?

Aleutian terns breed each year in western and southern Alaska, on the Aleutian Islands, and in parts of far-eastern Siberia, in the northern hemisphere summer, before migrating to southern wintering grounds.

Exactly where the elusive shorebirds spend the northern winter is a subject of some debate, with very little published information and previously recorded sightings of small numbers around south-east Asia.

It was passionate birdwatcher, Liam Murphy, who first spotted the Aleutian terns in Australia, at Farquhar Inlet, Old Bar, on the New South Wales mid-north coast in December 2017.

He went looking for them after realising he had inadvertently photographed them a year earlier.

"I was looking through some old photos and I found a photo that I remembered taking, but I couldn't figure out what the birds were, so I posted it to a Facebook bird identification group where it was suggested they looked like Aleutian terns," Mr Murphy said.

"It was really just a happy accident I guess."

"I went back to the same spot exactly 12 months later and the birds were there again, and they stayed the whole summer, and there were up to 18 birds, it was amazing," he said.

Sighting significant for bird researchers

The sighting led to a flurry of excitement among birdwatchers and some flew in from other states to catch a glimpse of the Aleutian terns.

"There was obviously a lot of excitement, it's not often a new species turns up that has never been seen before, especially on the Australian mainland," Mr Murphy said.

"Hundreds of people came to see those birds over the course of the summer."

Mick Roderick with Birdlife Australia said the sighting was considered very significant by bird researchers, who for years have been trying to find out more about the elusive birds.

"It's a very enigmatic species really, we still don't have a full understanding of what these birds do and people in Alaska are studying them very closely, so these records of birds in Australia is of great interest to them," he said.

"Apart from the Old Bar sightings there has barely been another record of Aleutian terns in the southern hemisphere, it's quite remarkable."

"Some birds that have been tracked by these Alaskan researchers have made their way towards the Queensland coast and there's a handful of records around the eastern side of New Guinea, but this is really an isolated record for Australia."

It's now thought the birds may have in fact been visiting Australia for many years, but no-one had noticed, as they are superficially similar to common terns, which can be seen in their hundreds at Old Bar's Farquhar inlet.

"That's definitely possible, in fact a few people, including myself have gone back through photos, looking for hidden Aleutian terns in those photos, but we can't find any evidence," Mr Roderick said.

"So there's two explanations, one, the birds haven't been doing this and this is a new thing, or they've gone overlooked, we really don't know."

Little terns need protecting

The Old Bar area where the Aleutian terns were sighted is also a nesting site for an endangered colony of Little terns, and efforts are underway by the local council, community volunteers and the National Parks and Wildlife Service to ensure they are protected, especially if there is another influx of birdwatchers to the area.

Last year was a disastrous breeding season for the Little tern colony and only one chick survived.

"The Little terns face all sorts of challenges, nesting on a beach, there's interactions with dogs and four-wheel-drives, people, high tides, all sorts of things, so we just need to be mindful there is a breeding threatened species in the area trying to do their thing," Mr Roderick said.

Birdwatchers have their binoculars ready

Meanwhile, birdwatchers are waiting and hoping the Aleutian terns will soon again end their epic migration in Australia.